The invention has among its objects the provision of a multilayer semiconductor element with improved dynamic electric parameters, while simultaneously maintaining a high level of static parameters, particularly the blocking and reverse voltage and the possibility of sustaining a high current load.
Similar elements of known design use microleaks between the cathode and the second external layer for the improvement of the parameters du/dt of the network. For the improvement of the parameters di/dt and of switching properties, a special arrangement of the control zone is used, for instance an auxiliary emitter layer provided with an auxiliary contact forming an auxiliary structure for cascade switching. In order to reduce the turn-off time, a regulation of the lifetime of minority carriers is used, for instance by diffusion of gold or other components, by electron irradiation, by gamma irradiation and the like.
A drawback of these arrangements is that the individual constructional designs aim at an improvement of one kind of parameters, while other parameters are influenced rather unfavorably. A special design of the control zone of components of known arrangements for instance yields a high value of the parameters di/dt; it does not, however, solve the problem of the turn-off time. In order to achieve a short turn-off time, a substantial reduction of the minority carriers has to be used. This influences adversely the value di/dt, mainly leading to an impairing of the dependence on temperature of the reverse and blocking characteristics of the element, and also leads to a reduction of the possibility of sustaining a high current load. In addition, the achievement of the required concentration profile of generation-recombiningadmixtures is rather demanding technologically, whether a diffusion of some recombination admixture is used, or recombination centers are formed by radiation.